From Sega Retro
Bloxeed is a 1989 arcade puzzle game by Elorg and Sega based on Tetris. It was first released exclusively in Japan on System 18 hardware before Sega ported it to their System C hardware for international release; it was the first System C game to be released. The game wasn't ported to non-arcade systems at the time, but was packaed with Tetris and Flash Point in Sega Ages 2500 Series Vol. 28: Tetris Collection.
The game plays like Tetris — pieces of four blocks fall from the top of the well, and making a horizontal row full of blocks clears that row and moves everything above down a row. After some time, one almost full row of blocks will pop up from the bottom. Furthermore, some blocks have numbers or letters on them. These blocks are called "Power Blocks." Clearing the row with the Power Block in it will have some effect, depending on the number/letter shown:
In two-player mode, clearing two or more rows will knock whatever piece is currently falling in your opponent's well out and send most of the blocks of those two rows back at him.